1. Field of the Invention
The present invention relates to a magnetic device and a frequency detector.
2. Related Background of the Invention
As a magnetoresistive effect element, a GMR (Giant Magnetoresistive) element comprising a nonmagnetic conductive layer interposed between a fixed layer whose magnetization direction is fixed and a magnetization free layer whose magnetization direction varies freely is known. Moreover, as another magnetoresistive effect element, a TMR (Tunnel Magnetoresistive) element comprising a nonmagnetic insulating layer interposed between the fixed layer and the magnetization free layer is known. A current fed through such a magnetoresistive effect element provides a spin-polarized current, which then interacts with a spin accumulated within the magnetization free layer to generate a torque, and as a result the magnetization direction of the magnetization free layer will vary depending on the polarity of the spin-polarized current. In the magnetization free layer disposed within a certain magnetic field, even if attempting to change its magnetization direction, a torque will work in the magnetization direction so as to restore the magnetization direction to a stable direction constrained by the magnetic field. Movement of this magnetization direction is analogous to the swinging oscillation of a weight of a pendulum when the weight of the pendulum pulled by gravity is swung by a certain force, and this is called a precession movement.
Recently, a phenomenon has been discovered that a resonance occurs when the natural frequency of precession movement of this magnetization direction coincides with the frequency of an AC current flowing through the magnetization free layer (see Nature, Vol. 438, 17 November, 2005, pp. 339-342). The resistance value of the TMR element depends on the angle formed between the magnetization direction of the magnetization free layer and the magnetization direction of the fixed layer. If the resonance in the magnetization direction occurs in the magnetization free layer, the magnetization direction of the magnetization free layer will oscillate greatly and the resistance value of the TMR element will periodically vary greatly. On the other hand, if the resistance value of the TMR element varies greatly in synchronization with the input AC current, the AC current flowing between both ends of the TMR element will vary asymmetrically with respect to the zero level and accordingly have a DC component, and this varying portion can be extracted as an output (the spin torque diode effect).